The present invention relates to an improved valve structure for a shock absorbing device. More particularly, the present invention relates to a simplified, more economical valve stem and compression head assembly for shock absorbing devices, especially for shock absorbing vehicle struts. As used herein, "shock absorbing device" refers to both conventional shock absorbers and struts, as well as replacement cartridges for struts.
As known to those of skill in the art, conventional shock absorbers are generally used in vehicular suspension systems wherein the tire wheel attaches to a spindle which, in turn, joins upper and lower control arms. A spring works between the vehicle frame and one of the control arms to provide biased support for the weight of the vehicle. The shock absorber controls oscillations of the spring.
A strut assembly is generally used in a vehicular suspension system that eliminates the spindle, the upper control arm, and the related components. The strut attaches directly between the lower control arm and the car body, to support the weight of the vehicle and to control oscillations of movement. The strut assembly has become much favored for suspension systems in recent years because it provides a much lighter, more space efficient design.
Conventional shock absorbers and struts both provide shock dampening action by placing a moving piston in a defined fluid chamber and restricting the flow of fluid within the chamber in response to the piston movement. Conventional shock absorbers and struts both have valving systems in the bottom of the shock absorbing structure, i.e., compression head assemblies, to help control the flow of fluid in the chamber. When the piston moves downward in the chamber, fluid flows out of the lower portion of the chamber; in such a sequence, the shock absorbing device is referred to as being in a "compression mode." When the piston moves upward in the chamber, fluid flows back into the lower portion of the chamber; in this sequence, the shock absorbing device is referred to as being in a "recoil mode."
The compression head assemblies in conventional shock absorbers typically have a dual valve port design. A first valve in a first valve port acts as a compression valve to permit fluid to flow out of the chamber when the device is in a compression mode. A second valve and valve port acts as a replenishing valve, to permit fluid to flow back into the chamber when the device is in a recoil mode. Representative designs of such shock absorbers are shown in Szostak, U.S. Pat. No. 3,127,958 and Damon, U.S. Pat. Nos. 3,181,656 and 3,213,973.
The compression valve components of dual element valve assemblies are sometimes manufactured by a relatively fast and efficient metal stamping operation. Such a valve stem and method is shown in Pepi, U.S. Pat. No. 4,182,438.
Struts differ from conventional shock absorbers with respect to several internal configurations. Since the strut is a load bearing member of the suspension system, whereas the conventional shock absorber is not, the piston and related members of a strut are bigger and stronger than are the comparable members of a shock absorber. One result is that a substantially greater volume of fluid flows in and out of the strut's fluid chamber than flows in and out of the shock absorber's fluid chamber, as the piston moves up and down in the chamber. In order to accommodate the greater fluid flow, the valving for the compression head in a strut requires larger openings than the comparable valving for the compression head assembly of a conventional shock absorber. In order to make room for the larger openings, struts generally have a single port compression head design. That is, a single valve defines both a first passageway for fluid flow out of the chamber during the compression mode and second passageway for fluid flow into the chamber during the recoil mode. Of course, the combination valve element design might also be used in a conventional shock absorber. Representative designs of a single element structure as shown in De Koning et al., U.S. Pat. No. 2,849,090, Palmer, U.S. Pat. No. 3,757,910, and a French Pat. No. 1,058,601.